48 GENERAL HISTORY OF THE INFUSORIA. 



N. Nitzschii, N. lanceolata, and N. capitata ; also Gomplionema truncatum, 

 Cocconema cistula, Arthrodesmus quadricattclatus, and Clostei^imn acerosum. 

 The two last, however, are Desmidieae. In the seven species of Navicula 

 enumerated, fi'om 4 to 20 little stomach- sacs are said to have become filled 

 with the indigo employed as the colouring matter. 



*' This effect (as Meneghini remarks) could only be produced by keeping the 

 Diatomeae a long time in water laden ^vith particles of indigo, and often re- 

 newed." Kiitzing deduced an opposite conclusion from these experiments, 

 viz. that they were solid corpuscles which, being seated near an opening, 

 exerted an especial attraction upon the colouring matter. Meyen argued, 

 so long since as 1839 {Jahreshericht d. Akad. Berlin), against the supposed 

 stomach-sacs and the entrance of colouring matter within them. His 

 objections are thus expressed : — " On the one hand, I can see no stomach-sacs 

 in the Naviculce, and never observed in the living and moving Bacillaria the 

 colouring matter received at one extremity and carried towards the centre, 

 where these stomach-sacs should lie, whilst among the ciliated Infusoria 

 such observations are easy ; on the other hand, it is not uncommon, especially 

 in the larger species, to see the molecules of the colouring matter employed, 

 lie upon the middle of the broad ventral surface, looking as if actually within 

 the organism ; but if a glass plate be placed upon the specimen and then 

 carefully removed, the particles of colouring matter are taken away with it." 

 Even Ehrenberg admitted that the presumed stomach-sacs varied in number, 

 were quite irregular in their disposition in the interior, and not unfrequently 

 wanting altogether. This last circumstance, Kiitzing remarks, is opposed to 

 the belief in their digestive functions, since such important organs as stomachs 

 can never be supposed absent. 



Although the existence of this fanciful polygastric apparatus in the 

 DiatomeaB is scarcely worth controverting, yet we may add to the above 

 objections to it the fact that, in the hands of other experimenters, the 

 attempt to introduce colouring matter by any definite apertures into the 

 frustules of this family has been unsuccessftd. 



The arrangement of the mucilaginous endochrome, or rather of its pro- 

 minent globules, vesicles, and granules, is sufficiently definite and constant 

 in the same species to afford useful characteristics. At one time these 

 molecules are diffused rather irregularly ; at another they are collected in a 

 rounded heap towards the centre, whilst at another they are disposed in 

 lines radiating from the nucleus, or formed in a layer upon the cell-waU, — 

 ** at all times " (adds Prof. Smith) " having one or several oily globules, 

 which occupy in different species different positions, but are constant in 

 number and position in the same species. The minute granules " (he con- 

 tinues, i. p. 20) " are generally accumulated in thin layers towards the internal 

 cell-waUs : when the frustule is so turned that this layer of endochrome is 

 presented edgeways to the eye, the granules appear to be chiefly aggregated 

 into two plates applied to the opposite sides of the frustule ; and when self- 

 division is in progress and the cell-contents are divided into two portions, 

 such a separation or temporary aggregation must necessarily ensue ; but in 

 the simplest condition of the fi^ustule the contents are diffused over the entire 

 surface of the cell- walls, precisely as may be seen in the cells of many of the 

 larger Algae, or of some water-plants of a higher order, as in the leaves of 

 Hydrocharis Morsus-rcmce and others." 



Schultze has recently represented (Milll. ArcMv, 1858) a definite peculiar 

 disposition of the endochrome — of its mucilaginous and granular portions and 

 its' coloured corpuscles. In the more or less quadrate frustules of Denticellay 

 and in the circular ones of Coscinodiscus, he describes the existence of a central 



